Nonionic cellulose ethers are generally known in the art. They are employed in a variety of industrial applications, as thickeners, as water retention aids, and as suspension aids in certain polymerization processes, among others.
U.S. Pat. No. 4,784,693 discloses the use of hydrophobically modified hydroxyethyl cellulose (HmHEC) having 0.2-4 weight percent hydrophobic substitution, an MS (hydroxyethyl) substitution of 1.5-4 and a viscosity of 300-500 cps, measured as a 1 wt.-% aqueous solution, for use as a fluid-loss additive in oil-well cementing.
U.S. Pat. No. 4,529,523 discloses the use of hydrophobically modified cellulose ethers, such as hydrophobically-modified hydroxyethyl cellulose having about 1 weight percent hydrophobic substitution, an MS (hydroxyethoxyl) substitution of 2.5 and molecular weights of 50,000-1,000,000, preferably about 150,000-800,000, as water flooding medium for the recovery of petroleum.
U.S. Pat. No. 4,228,277 discloses nonionic methyl, hydroxyethyl or hydroxypropyl cellulose ethers substituted with long chain alkyl radicals having 10 to 24 carbon atoms in an amount between about 0.2 weight percent and the amount which renders the cellulose ether less than 1% by weight soluble in water. The products exhibit improved viscosifying behavior compared to their unmodified cellulose ether counterparts.
Unfortunately, many of the known water-soluble or water-swellable cellulose ethers used as rheology modifiers or thickening agents exhibit a reversible loss of viscosity at elevated temperatures, referred to as thermal thinning. However, in many end-use applications, such as water, petroleum and natural gas recovery (e.g., cementing wells, hydraulic fracturing, and enhanced oil recovery), geothermal wells (fracturing and cementing), construction (e.g., concrete pumping and casting, self-leveling cement, extruded concrete panels), full-depth road reclamation, ceramics (e.g., as green strength additive), metal working and cutting fluids, thermal thinning is highly undesirable. Accordingly, it would be desirable to find new cellulose ethers which exhibit a reduced degree of thermal thinning and thus would be more efficient thickeners at elevated temperatures.